The Doctor gains Plantagenet's trust by saving his life and has him taken to the hospital. The Doctor asks to have the rock samples analysed and gets the research room reopened where Turlough & Norna discover an underground tunnel which Captain Revere had been using to gain rock samples. They explore the tunnel, and are followed by the Doctor & Range when they find them missing. Tegan finds evidence of "deaths unaccountable" but unobserved Plantagenet falls from his bed and is swallowed up by the ground. The Doctor & Range find Turlough in the tunnels raving about Tractators. The Doctor searches for Norna who he finds captured by the giant woodlice like Tractators but is apprehended trying to prevent Tegan from being captured.

That's a bit more like it, less arguing dislikeable colonists and more mysterious happenings as we get bodies being sucked into the ground. Special mention for Mark Strickson's acting here as he becomes increasingly disturbed in the tunnels by something that's bringing back old memories. But yet another slow moving shuffling monster.....